Incorporation of black and white developing agents such as hydroquinones, aminophenols, and phenidones, or color developing agents such as p-phenylenediamine derivatives, in a light-sensitive material has been widely employed so that satisfactory development can be attained even under very rapid developing conditions. (e.g., 30 seconds or less) It is also known that brightening agents can be applied to a silver halide photographic printing paper in order to increase the whiteness of the background of the paper after rapid processing. Particularly in rapid processing, in which the processing time is short, residual color resulting from sensitizing dyes and dyestuffs, for example, is liable to develop. Under such conditions, therefore, increasing whiteness is a significant requirement for providing a printing paper having a good appearance.
Brightening methods are, of course, generally applicable to increase whiteness irrespective of the presence of residual color.
The following brightening methods have heretofore been known: adding brightening agents to a paper support or a polyethylene layer laminated on the support; adding water-soluble or oil-soluble brightening agents to a silver halide emulsion layer or other photographic layers; and using a developer in which brightening agents have been incorporated.
In the case of a polyethylene-laminated paper, for example, which is suitable for rapid processing, if a brightening agent is incorporated into the polyethylene layer, it is readily decomposed during melt extrusion process of the polyethylene layer because of its poor heat stability. If a brightening agent is attempted to be added during development, no uniform finishing can be attained unless the concentration of the brightening agent is always maintained at a constant level. Thus, it is most preferred to incorporate brightening agents in photographic layers. In this method, oil-soluble brightening agents are effectively incorporated rather than water-soluble ones because the former do not elute out of the photographic layer during developing. For this purpose, British Pat. No. 1,072,915, for example, discloses a method in which water-soluble brightening agents are dissolved in organic solvents and then added to a gelatin layer in the form of dispersions. As these organic solvents, tributhyl phosphate and diethyl phthalate, for example, are used. It is also known that amide compounds as described in U.S. Pat. No. 2,322,027, for example, are suitable as organic solvents for use in emulsification of brightening agents.
In the case of light-sensitive materials containing developing agents in the photographic layer thereof for the purpose of rapid development, for example, it has been discovered that even if brightening agents are dissolved in such organic solvents and applied in the form of dispersions, satisfactory whiteness cannot be obtained, although the reason for this is not clear. When, on the other hand, water-soluble brightening agents as described in Japanese Patent Publication No. 30495/73, for example, are added to the photographic layer, the above phenomenon that the whiteness-increaseing effect is reduced by the presence of developing agents does not occur. Instead, other disadvantages are encountered in this case, for example, since the brightening agents, as described above, elute out during development, whiteness cannot be increased to an extent that is expected, and the whiteness varies depending on processing conditions.